This project investigates the interaction between reward and cognition. There is evidence that the prefrontal cortex and basal ganglia work together to support reinforcement-based decision-making, and that psychoses may result from dysregulation of this circuitry. However, we know little about the physiological mechanisms through which brainstem reward systems might contribute to abstract thought. We plan to address this by recording activity in prefrontal cortex and striatum during a categorical decision-making task. The central question addressed by this proposal is How does knowledge about reward affect the representation of sensory evidence and decision criteria in the brain? One process that contributes to flexible decision-making is stimulus categorization. Categorization affords a flexible linkage between sensory stimuli and motor responses. Categorization improves the efficiency of decision-making because responses that are appropriate for one member of a class often generalize to other stimuli in the same category. Categorization requires that attention be directed to critical stimulus features that identify stimuli as being in the same or different classes. Some categories are innate or overlearned. But in many cases category boundaries must shift on the fly to adapt to changes in the environment. We will present preliminary evidence that a fronto-striatal network is involved in categorical decision-making. In this project, we will investigate how reinforcement modulates activity in this network during categorical decision-making and category learning. This work is highly relevant to many Psychiatric and Neurological disorders including Schizophrenia, Depression, Autism, Drug Addiction, Obsessive-Compulsive disorders, and Attention-deficit disorders (ADD and ADHD).